This invention relates generally to pumping apparatus, and more specifically relates to positive displacement pumps of the type utilized in dispensing metered quantities of flowable liquid compositions, such as, for example, epoxy resins or so forth.
In the course of dispensing flowable liquid materials, such as, for example, epoxy resins, metering pumps are commonly utilized, which are based upon displacement of some type of piston element a predetermined distance within a pressure chamber. The material to be dispensed is initially provided to the said chamber, so that for each movement of the piston a specified amount of the liquid material may be thus dispensed through a suitable outlet. It is common and well-known further, to utilize a plurality of such pumps in tandem, in those instances where it is desired to simultaneously dispense measured quantities of two or more components of a multi-component composition. Such is the case, for example, with the common epoxy resin systems, where one desires to dispense simultaneously the resin and a catalyst for same.
In applications of the aforementioned type, key requirements for the pumping device are simplicity of operation and dependability; and moreover, because the said pumps can be in semi-continuous, if not virtually continuous use, it is most important that they require an absolute minimum of down-time for maintenance, repair, or so forth.
A highly significant problem that has been evident in the prior art with respect to this type of devices, derives from the requirement for providing appropriate sealing between the slideable piston element, and the chamber volume which is pressurized in response to the piston movement. The sealing means utilized for these purposes should not only provide effective sealing action, but further, should have such characteristics as will enable it to operate in the stated environment for sustained periods without requiring replacement. Further, should such replacement be required, the operation ought to be conductable in a simple manner, preferably with minimization of down-time. It may be noted here that the problem of wear for this sealing means is particularly acute in many of the applications to which the present invention appertains, in that numerous of the epoxy and related compositions, are characterized by included fillers which take the form of finely dispersed quartz, fine sand, or so forth. These fillers, while serving admirable and necessary funtions in the dispensed compositions, are so thoroughly abrasive as to wear conventional sealing means at an alarming rate, which in turn requires replacement of such conventional seals at very frequent intervals.
Typically, for example, O-rings or similar solid cross-section sealing means have been utilized in the prior art in order to produce adequate sealing in the mentioned environment. An arrangement of this type, for example, is shown in U.S. Pat. NO. 3,802,805 which indeed discloses a typical example of a prior art type of device upon which the present invention improves. During piston displacement a high radial load is impressed on the O-ring seal; thus the sealing action is basically effected by section deformation of the said O-ring. Such approach, however, necessarily produces high friction and temperatures, with consequent high wear. Since, further, seals of this type provide no mechanism enabling substantial compensation for the said wear, the seals necessarily display a very short service life.
A further significant problem that has been noted in the prior art pertinent to the type of metering pumps considered herein, derives from the fact that numerous of the compositions with which apparatus of this type are utilized, are highly viscous in nature as, for example, many of the epoxy system components alluded to. As will be evident to those familiar with the present art, it is essential that a positive displacement metering pump include appropriate mechanisms as to assure that a full "shot" of the flowable composition is provided to the pressure chamber prior to displacement of the piston therein. Thus, voids within the "filled" chamber cannot be tolerated to any substantial degree, or unacceptable performance will ensue. Here, however, it may be noted that numerous of the prior art pumps intended for metering viscous materials have required use of unduly complex mechanisms for assuring complete filling of the pressure chamber, which mechanisms in turn have lent undue complexity and cost to the apparatus.
In accordance with the foregoing, it may be regarded as an object of the present invention, to provide a metering pump for dispensing measured quantities of a liquid composition, which includes sealing means which coact with a displaceable piston during pump actuation, as to provide effective sealing between the piston and a pressurization chamber from which the composition is expelled; and wherein the sealing arrangement is yet such that compensation for seal wear automatically occurs, thereby increasing the service life of the seal, and minimizing requirements for replacement or repair of same.
It is a further object of the present invention, to provide a metering pump particularly adapted for dispensing measured quantities of flowable liquid compositions, wherein features are incorporated enabling the sealing means between pressure chamber and moveable piston to be manually interchanged with standby seals of the same type, without requiring disassembling of the pump; and wherein the interchange operation renders the worn sealing means accessible for replacement without interfering with pump operation.
It is a yet further object of the present invention, to provide a metering pump, particularly adapted for dispensing measured quantities of viscous liquid compositions such as epoxy resins, or the like, which is so structured that the operation thereof assures provision of full shots of the viscous composition to the pressure chamber from which such composition is expelled.